An ablation catheter is a catheter having an end effector, such as a radio-frequency (RF) ablation head, designed to deliver energy to a target tissue for the purpose of forming a lesion on the target tissue. Catheter-based ablation therapy is performed by accessing the target tissue via a biological lumen, such as a blood vessel. The ablation head is often cooled with irrigation fluids to control the temperature of the ablation head. In some systems, the irrigation fluid is vented into the biological lumen or targeted organ via apertures in the ablation head. The local venting of irrigation fluid through the ablation head can serve the function of purging the immediate area of the target tissue, thereby preventing recirculation of blood proximate the ablation head that can lead to coagulation and the formation of blood clots.
An existing paradigm in irrigated ablation head design is to provide uniform flows through the purged apertures. For example, U.S. Patent Application Publication No. 2010/0030209 to Govari et al. (Govari) discloses an ablation catheter having a distal tip with a plurality of perforations through the outer surface, which are distributed circumferentially and longitudinally over the distal tip. Govari discloses that the perforations may optionally be varied over the length of the distal tip to compensate for pressure variation and ensure equal flow over the entire length. For this purpose, the perforations at and near the most distal part of the tip may be made larger than the more proximal perforations, which are nearer to the fluid inlet. As further example of the emphasis on uniform flow, U.S. Pat. No. 6,017,338 to Brucker, et al. discloses structures to uniformly and evenly distribute the fluid around tip structures.
U.S. Patent Application Publication No. 2008/0249522 to Pappone et al. discloses internal lumen designs in an irrigated catheter that promotes uniform cooling and/or uniform fluid distribution in longitudinally spaced apart elution holes by varying the diameter of a fluid delivery lumen.
Other designs, such as U.S. Pat. No. 7,104,989 to Skarda (Skarda) deliver greater flow to the tip region of the irrigated ablation head. Skarda discloses a plurality of pores arrayed longitudinally and circumferentially around all sides of the ablation head, with an increased density of pores in distal end region of the ablation head, thus concentrating delivery of a conductive fluid distally, where primary contact with the target tissue occurs.
Despite such designs, problems persist in the implementation of irrigated ablation heads. Such problems include coagulation of blood in recirculation zones about the ablation head that can lead to the formation of blood clots. There is need for an irrigated ablation catheter and system that mitigates these shortcomings.